Research On The Effect Of The Microwave On Starch Properties

Potato starch is the advantage resource in China. The rational using, conversionand industrial production of potato starch have great significance. The high contentstarch in potato possessing good quality and white color. Potato starch possess largeparticle size, high amylose content comparing with other starch. In this study,microwave was employed to deal with the potato starch, polarized light microscopyand scanning electron microscopy were used to observe the granule appearancemorphology of microwave starch. The pasting and rheological properties of potatostarch were studied by the rheometer and RVA. The texture changes of starch pasteand fried potato after microwave treatment was studied by the texture instrument todiscuss, in order to accumulate the data for the industrial application of potato starch’smicrowave treatment.The straight chain starch content, viscosity, solubility and swelling power,transparency, condensate sinking, chilled shrink of Potato starch andmicrowave-treated starch were studied. Along with the extension of the microwaveprocessing time, the amylose content, solubility, transparency, refrigerated shrink ofmicrowave starch showed the trend of first increase and then decrease,the swellingpower after the microwave treatment is less obvious. Microwave starch retrogradationis reduced with the prolongation of microwave time.Observation of starch by polarizing microscope, the original potato starchgranules showed an oval or round, clear polarization cross. The starch appearedshrunken and the polarization cross of the Shrunken starch disappears at microwaveradiation5s. Half of the starch appeared a pit and showed irregular particle shape andfibrous at microwave radiation10s. At microwave radiation15s, great part of thestarch changed into irregular shapes polarization cross. At microwave radiation20s,starch completely turned into irregular shapes or fibrous, cross-polarized completelydisappeared. By using of scanning electron microscopy, native starch was smoothwithout wrinkles and showed round or oval. At microwave radiation5s, the starchgranule surface wrinkled. The surface became rough and pits appeared at microwaveradiation10s. Starch had completely lost its original spherical appearance and most ofthe starch granules collapsed at microwave radiation15s. It became irregular starch granules at microwave radiation20s. The potato starch gelatinization retrogradationproperties and textural properties were measured at different microwave processingtime by RVA and texture analyzer. The results show that the gelatinization ofmicrowave potato starch reaches a minimum value of50.35°C at10s, attenuationvalues and regenerative value, respectively, maximum12159cp and4179cp. Theoriginal starch gel strength is59.234g, starch paste gel strength increases first andthen decreases In the microwave and reaches the maximum73.302g at3min in themicrowave.The rheological properties of potato starch paste by microwave treatment werestudied using TA Rheology Advantage(AR1000).The results showed that the staticrheological behavior of potato starch paste micriwaved displayed the pseudo plasticnon-Newtonian and shear-thinning fluid, which accord with the power law indexmodel and Cross model. The rheological behaviours of microwaved potato starchpaste were explained better by Cross equation than Power Law equation. The dynamicrheological behavior showed that the storage modulus (G’), loss modulus (G") ofpotato starch paste increased sharply from the microwaved time0~15s,but lossfactor(tanδ)decreased sharply. In the microwaved time15~20s, the storage modulus(G’), loss modulus (G") decreased sharply, loss factor(tanδ) increased sharply.The texture of potato chips treated by different microwave power, time, and theoil content of pre-fried French fries were studied by the Texture Analyzer. The optimalprocess of the microwave power, time and frying time is a microwave of596w,15sand the frying time of20s and the lowest oil content is13.22%. The oil content ofordinary fries is22.31%. The crushing strength of the microwave french fries was1150.453g, while ordinary French fries was711.143g by Texture Analyzer test.